Amputation of the arm causes significant disability, which is most effectively treated by replacement of the missing limb with a prosthetic device. Body-powered prostheses use a Bowden cable that couples motion of an intact joint to movement of the terminal device. Myoelectric prostheses control motorized joints via commands sent through the patients' residual muscles and sensed by surface electrodes embedded in the prosthetic socket.
Advances in embedded controllers, battery density, and motor design have increased the number of myoelectric prosthesis users. However, existing myoelectric prostheses are heavy, and wearing them constantly does not appeal to many amputees. Additionally, such prostheses are often too large for many amputees, such as children and many women. Several multi-function arms have recently come on the market, including Otto Bock's Michelangelo Hand, the Touch Bionics Hand, the BeBionics Hand, and the Vincent Hand. These devices are typically designed for a 50th percentile male (22.2 cm/8.75″ hand circumference). Other hands are being developed in research, but use components that limit the strength, weight, and small volumes the limbs can achieve.